1. Field of the Invention
This invention relates to liquid desiccant regeneration systems for use in air-conditioning systems, and is directed more specifically to a single stage desiccant regeneration system including a falling film heat exchanger.
2. Description of the Prior Art
Devices that use hygroscopic liquids, such as lithium chloride (LiCl), to dehumidify air are well known in the art. One of the principal limitations of such systems is the need to regenerate the desiccant once it has become diluted through absorption of water. Regeneration usually requires heating the desiccant to drive off the excess moisture, or exposing the desiccant to a hot gas which absorbs the excess moisture. Regenerators in which air serves as the hot gas are often employed, but are expensive to run, especially when waste heat for heating the air is not readily available. Boiler-type regenerators are also used, but are expensive inasmuch as a heating means must be provided and non-corrosive metals must be employed. An improved boiler-type regenerator is disclosed in U.S. Pat. No. 4,939,906 to Spatz, et al, which uses natural circulation of the desiccant being heated. The boiler in the '906 patent is provided with finned tubes through which desiccant being heated passes in an upward direction. The finned tubes are inside a housing containing gas combustion products which serve as a heat source for the boiler. Natural circulation is achieved by providing downcomer tubes which are outside the housing and at a lower temperature. The '906 patent also discloses a means for preheating the diluted desiccant before it enters the boiler for final regeneration. The means employed comprises a two-stage heat-exchanger for transferring heat from concentrated desiccant exiting the boiler to dilute desiccant exiting the air conditioner. The heat transfer takes place in a heat exchanger formed by stacking corrugated plates to form alternating flow channels--one for diluted desiccant and one for concentrated desiccant. The plates are sealed from each other by gasketing. Although the system provides for higher efficiency and lower costs, it is not without drawbacks. The need for gasketing to seal the plates from each other causes pressure to build up unevenly in the flow channels, which can lead to formation of "hot spots" and, thus, lower heat transfer efficiency.